1. Field of the Invention
The present invention relates to a magnetic recording medium and a method of manufacturing the same, and more particularly, to a magnetic recording medium with good dimensional stability, and to a method capable of stably manufacturing a magnetic recording medium of good dimensional stability.
2. Discussion of the Background
With the widespread use of personal computers, work stations, and the like in recent years, a large amount of research has been conducted in the field of magnetic tapes into magnetic recording media for use in recording computer data as external recording media. In the course of putting such magnetic recording media to practical use, a strong need has developed for greater recording capacity to achieve recording devices of greater capacity and smaller size. This has been particularly true in conjunction with reducing computer size and increasing information processing capability.
There has been a tendency to narrow the recording and reproduction track widths of magnetic recording media to achieve higher recording density and greater recording capacity. The thinning of magnetic tapes to permit high density recording has progressed in the field of magnetic tapes, with numerous magnetic tapes with a total thickness of 10 micrometers or less having appeared. However, as the thickness of a magnetic recording medium is reduced, it tends to be affected by changes in tension, heat, and humidity during storage, running, and the like.
That is, during recording and reproduction in magnetic recording and reproduction systems employing linear recording methods, the head moves in the width direction of the magnetic tape to select a track. As the track width becomes narrow, high precision becomes necessary to control the position of the head relative to the magnetic tape. Even when a narrow track is realized, variation in temperature and humidity in the use environment and in tension within the drive may distort the magnetic recording medium, in some cases precluding the reproduction head from reading tracks that have been recorded. Thus, there is a need for a magnetic recording medium affording better dimensional stability than what has been achieved thus far. To maintain stable recording and reproduction in such a high-density magnetic recording medium, greater dimensional stability is needed than that afforded by conventional media.
Accordingly, it has been proposed that the heat absorption level based on enthalpy relaxation be kept below a prescribed level due to noncrystalline portions (amorphous portions) by conducting a heat treatment at a temperature at or below the glass transition temperature of the nonmagnetic support (for example, see Japanese Unexamined Patent Publication (KOKAI) Heisei No. 11-110735, Japanese Unexamined Patent Publication (KOKAI) No. 2007-188613 or English language family member US 2007/166571 A1, which are expressly incorporated herein by reference in their entirety ).
Japanese Unexamined Patent Publication (KOKAI) Heisei No. 11-110735 describes relaxing enthalpy by subjecting a polyethylene terephthalate support with a glass transition temperature Tg of 70° C. to a heat treatment at 60° C. However, by the method described in this application, even when it is possible to relax enthalpy and achieve dimensional stability in the support, it is impossible to obtain a support having adequate strength due to the low glass transition temperature of the support. Japanese Unexamined Patent Publication (KOKAI) No. 2007-188613 describes relaxing enthalpy by subjecting a polyethylene terephthalate support with a glass transition temperature of 125° C. to a heat treatment at 110° C. However, investigation by the present inventors has revealed that it is sometimes difficult to stably produce a magnetic recording medium by the technique described in this application due to sticking of the tape when the heat treatment step to relax enthalpy is conducted with the stock material of the magnetic recording medium in a rolled-up state following formation of the magnetic layer.